This invention relates to the control of fluid flow using a check valve responding to fluid injected into the valve by devices such as Luer fittings or cannulas.
Check valves are used extensively in medical applications, such as for intravenous delivery of fluids. In some cases it may be desirable to open the valve by using fluid pressure. In other cases, it may be desirable to open the valve using means other than fluid pressure. Thus, a user may wish to open the valve independently of the presence or extent of fluid pressure, in preparation for anticipated fluid flow. For example, it may be desirable to maintain the valve in its open position for a prescribed interval of time independently of whether fluid flow is present. Another example of a situation in which it is desired that a check valve be open irrespective of fluid pressure is that in which a check valve is connected to a catheter inserted in a patient and it is desired to sample blood or other fluid by opening the check valve and inducing a reverse fluid flow that ordinarily would be checked or stopped by the valve.
In medical applications, it is often desirable to introduce a dosage of drugs into an existing flow of a fluid such as dextrose solution. This is often accomplished by using a syringe with a needle penetrating a rubber seal over a branch of a "Y"-connector. Because of the possibility of needle-induced infections, however, the current trend is to minimize the use of needles and to favor the use of blunt cannulas or Luer fittings.
Prior art check valves providing for the use of wide cannulas or Luer fittings to open the valves have been of the general configuration using a resilient disk situated in a flow channel, supported at the center and pressed at its periphery against a valve seat by the resiliency of the disk and back pressure from downstream fluid. This type of valve is opened by forward pressure applied radially outward of the center but inward of the valve seat either by forward fluid flow or by a separate plunger which acts as an extension of the cannula or Luer fitting.
These valves suffer from a number of disadvantages. First, there is the problem of the plunger collecting debris such as clotted blood that may interfere with the operation of the valve, in a worst case situation applying enough forward bias to crack open the valve unintentionally.
Second, the additional plunger component not only adds to cost in fabrication of the component, but in handling and assembly. The additional component adds the possibility of omission in assembly, resulting in a conventional check valve opened only by forward fluid pressure if the plunger is omitted or in no valve at all if the disk is omitted.
Third, dimensional variations in the multiple cannulas or Luer fittings that may be used with a single valve may result in different operation of the valve. In the worst case, a plunger may be forced against the disk with such force as to damage the disk, and thus the valve.